Iron oxide synthesized by the Adam's fusion method as the negative electrode for iron-air batteries

Lithium-ion technology presents several disadvantages that hinder the mass introduction of electric vehicles. In this regard, novel approaches and chemistries have been developed with the aim of improving the current features. Among these new technologies, metal-air batteries are receiving especial interest, given that they are capable of very high theoretical energy densities. Iron-air batteries belong to the category of metal-air batteries, in which the anode or negative electrode is formed by a metal and the cathode or positive electrode is a porous air breathing composite material. Having only one reactant contained inside the cell, metal-air batteries permit much more compact and lighter designs and therefore, they are capable of very high energy densities. In the case of iron-air batteries, the cells are composed by an iron negative electrode, a bifunctional air positive electrode and an aqueous potassium hydroxide (KOH) electrolyte. As both the positive and negative electrodes are immersed in the same electrolyte, there are no separating membranes required [1, 2]. The iron oxidation is a surface reaction, and so it is prone to passivation. This issue can be addressed by increasing the electrochemical specific surface of the iron anode, by means of the use of carbon nanomaterials with a porous nanostructure that maximizes the usability of the electrode [3-6]. In the present work, iron oxide has been synthesized by a new methodology based on the Adam's fusion method, usually employed for the production of fine noble metal oxide powders [7]. This method is based on the oxidation of metal precursors in a molten nitrate melt. The so-obtained iron oxide was mixed with different amounts of carbon and tested in a half-cell system with a 6M KOH solution as electrolyte.